@jenya7
Yes it means, open the .pro file (the project file)
and insert that line on top
It adds the module called bluetooth
Often it already adds gui that way.
like
QT += core gui
so you just add it to the line (only bluetooth)
or on its own line with full syntax as he wrote.

small note:

QBluetoothDeviceDiscoveryAgent *discoveryAgent = new BluetoothDeviceDiscoveryAgent();
discoveryAgent.start(); <<--
should be
discoveryAgent->start();

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